The similar issue was noticed and fixed earlier for the user profiles.

But it still can be seeing on the StackExchange "All Sites" page. I almost sure that is was already submitted here, but i cannot find any question about this. And, yes, I understand that 12 months are most likely 11 months with some additional days, and 1 year is 1 year with some additional days, but when you see it on the screen, it looks a little bit odd.

This doesn't look like a rounding issue. I think it's just like the question author purports in being the same issue as with profile fields. The only 2 sites with "12 months" were launched on July 26th and July 28th respectively, and today is July 25th which is within the 5 day window between 360 days (12 30-day periods) and 365 days (an actual year). If rounding were the case, Money (launched on August 4th, 10 days from now) should be showing 12 months, but it is showing 11 months. The fix will probably be the same thing waffles did last time.
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Grace Note♦Jul 25 '11 at 12:40